Kaiser Aluminum indefinitely postponed its previously announced initial public offering.
Sproul also served as a director of Kaiser Aluminum and Chemical Corporation.
Kaiser Aluminum agreed to build the dam for Nkrumah, but restricted what could be produced using the power generated.
Kaiser Aluminum offers seven other pension plans to its hourly and union workers, and those plans are still operational for now.
Fourth-quarter sales rose 6.3 percent, to $544.6 million from $512.5 million, Kaiser Aluminum said.
For the full year, Kaiser Aluminum lost $32.7 million, down from a loss of $186.5 million in 1985.
Among the companies that labor unions are boycotting is Kaiser Aluminum, which locked out 2,900 unionized workers 14 months ago.
The 220-foot tower was once used by Kaiser Aluminum in the making of coated aluminum wire.
The plan for salaried workers at Kaiser Aluminum was all the way down to 21 cents for each promised dollar.
"We now are the third-largest customer of Kaiser Aluminum," he said.